1. Field of the Invention
The present invention relates to hollow polyester fibers, having a high recovery from compression of the hollow portions of the fibers by external force, and textile articles comprising the hollow polyester fibers, which articles include woven or knitted fabrics having excellent form retention, pile sheet materials having a high recovery of piles from prostration thereof, nonwoven fabrics having a high bulkiness, a soft feeling, a high warm-keeping property and a high resistance to compression and fatigue, and artificial leather materials having good recovery from mechanical deformation.
2. Description of the Prior Art
Hollow polyester fibers having a hollow volume of 40% or more based on the total volume of the fibers are well known.
The hollow polyester fibers can be produced by extracting a melt of a polyester resin through an arc-shaped spinning slit.
To increase the hollow volume of the hollow fibers, usually, the radius of curvature of the arc-shaped slit is increased and the width of the slit is decreased. However, the practical lower limit of the width of the slit is 0.05 to 0.03 mm, because when the slit width is smaller than the above-mentioned practical lower limit, the slit is easily blocked by contaminating solid particles in the polyester resin melt. Also, if the slit width is too large, the extrusion rate of the polyester resin melt per spinning slit is increased, and the resultant fibers have an increased tex (denier). Thus, hollow polyester fibers having a hollow volume of 40% or more can be produced only under limited spinning conditions. In other words, under some spinning conditions, hollow polyester fibers having a hollow volume of 40% or more cannot be obtained.
Also, the conventional hollow polyester fibers having a high hollow volume of 40% or more are disadvantageous in that the hollow polyester fibers are easily compressed and flattened in a fiber-forming procedure and after-processing procedure, and the flattened hollow polyester fibers are difficult to recover the original hollow fiber form, and thus have no effect as hollow fibers. The conventional hollow polyester fibers produced by a process in which a polyester resin melt is extruded through a plurality of hollow fiber-forming slits and the extruded hollow filamentary polyester resin melt streams are drafted and solidified and the resultant undrawn hollow fibers are drawn under conventional fiber-producing conditions, as disclosed in Japanese Unexamined Patent Publications No. 61-79,486, No. 61-83,307, No. 6-2,210, No. 6-235,120, No. 7-238,418, No. 7-238,419, No. 7-268,726 and No. 7-268,727, or by a process in which high hollow polyester fibers are produced by using a specific spinning orifice in which a plurality of slits are connected with each other into a complicated pattern, as disclosed in Japanese Unexamined Patent Publication No. 62-206,009, are disadvantageous in that the polyester crystals in the fibers have a small crystal size in (010) plane, and when the hollow fibers are compressed and flattened, the flattened fibers are difficult to return to the original hollow fiber form.
In another process for producing hollow polyester fibers, as disclosed in Japanese Examined Patent Publications No. 57-54,568 and No. 62-33,915, the hollow fibers are produced at a high spinning speed of, for example, 3000 m/min. or more. This process contributes to increasing the crystal size of the polyester crystals to a small extent. However, the process is still disadvantageous in that the hollow fibers are easily flattened in the spinning procedure and the after-processing procedure. Therefore, this process is not utilized to produce high hollow polyester fibers having a hollow volume of 40% or more.
In another process, as disclosed in Japanese Unexamined Patent Publication No. 6-287,809, hollow polyester fibers are produced by melt-spinning a polyester resin into hollow polyester fibers at a spinning draft of 400 to 4000 at a spinning speed of 1500 m/min. or less, while blowing a cooling gas toward one side of the hollow polyester fibers. Also, in another process, as disclosed in Japanese Unexamined Patent Publications No. 01-47,807 and No. 62-206,008, hollow polyester fibers are produced at a spinning speed of 1500 m/min. or less while rapidly cooling extruded polyester resin hollow filamentary streams at one side thereof. In the publications, it is asserted that the process can produce high hollow polyester fibers having a hollow volume of up to about 60%. However, when the hollow volume is increased to more than 40%, in practice, the resultant hollow fibers are easily flattened in the melt-spinning procedure and the after-processing procedure. Also, the polyester crystal size of the resultant hollow polyester fibers is larger than that produced by the process as disclosed in the above-mentioned Japanese Unexamined Patent Publications No. 61-79,486, No. 61-83,307, No. 6-2,210, No. 6-235,120, No. 7-238,418, No. 7-238,419, No. 7-268,726 and No. 7-268,727. However, the crystal size in the (010) plane is less than 4.0 nm and is still unsatisfactory. Further, the hollow fibers as disclosed in the above-mentioned publications are still disadvantageous in that when the hollow volume is more than 40%, the resultant hollow polyester fibers have various problems derived from the crushing and flattening thereof, and the hollow volume of the hollow fibers is easily changed by external force applied thereto during usage. Therefore, the hollow fibers produced by the above-mentioned process and having a hollow volume of more than 40% have not yet been employed in practice.
Japanese Unexamined Patent Publications No. 57-106,708, No. 62-289,642 and No. 63-21,914 disclose another process for producing synthetic hollow fibers. In the process, hollow filamentary resin melt streams are extruded through a hollow filament-forming slit-shaped nozzle, while introducing an inert gas such as nitrogen gas from the inside of the nozzle to cool the outside and inside of the hollow filamentary resin melt stream, or hollow filamentary resin melt streams are extruded through double pipe-formed spinning orifices, while introducing spontaneously or compulsorily a cooling gas such as air or nitrogen gas from the nozzle into the core portions of the extruded hollow filamentary streams. The process can produce hollow polyester fibers with a high hollow volume of 40 to 70%. However, the crystal size in (010) plane of the polyester crystals is small and thus when the hollow fibers are deformed or flattened, the deformed or flattened hollow fibers are difficult to return to the original form. Also, this process is disadvantageous in that since the spinning orifices or nozzles have a complicated constitution and thus the number of the orifices or nozzles is difficult to increase, and thus the productivity of the hollow fibers is very low and the cost of the hollow fibers is very high. Also, the complicated spinning orifices or nozzles are suitable to produce thick hollow fibers having a thickness of 33.3 d tex (30 denier) or more but not appropriate to produce thin hollow fiber having a thickness of 4.4 to 5.6 d tex (4 to 5 denier) or less. Accordingly, hollow polyester fibers having a small thickness of 8.9 d tex (8.0 denier) or less and a hollow volume of 40% or more have not yet been practically provided.
As mentioned above, the hollow polyester fibers having a small thickness of 8.9 d tex (8.0 denier) and a high hollow volume of 40% or more and exhibiting a high recovery from compression or flattening were not available in practice before the present invention.